US2212851A - System for amplifying electrical oscillations - Google Patents

Description

Aug. 27, 1940. A. VAN DER ZIEL SYSTEM FOR AMPLIEYING ELECTRICAL OSCILLATIONS Filed Sept. 26, 1936 -u a 1 my a A V 9 I R C Ab-ABET L INVENTOR A. VAN 0 I? Z/EL BY Mam ATTORNEY Patented Aug. 27, 1940 UNITED STATES SYSTEM FOR ANIPLIFYING ELECTRICAL OSCILLATIONS Aldert van der Zicl, Eindhoven, Netherlands, assign'or, by mesne assignmentato Radio Corporation of America,

poration of Delaware New York, N. Y., a cor- Application September 26, 1936, Serial No. 102,727

In Germany October 18, 1935 i 7 Claims.

The invention relates to amplifying systems for very high frequencies wherein the control grid and the cathode of one or more amplifying tubes are connected to a tuned oscillatory circuit.

When voltages of very high frequency are applied to the electrodes of a thermionic tube, damping occurs, as is well-known, between the control grid and the cathode of the tube due to the fact that the transit time of the electrons is not negligibly small with respect to the period of the voltages applied. This damping, which is hereinafter referred to as transit time damping, has been calculated by C. J. Bakker and G. de Vries in an article: On vacuum tube elec- 15? tronics published in Physica 2, pages 6834597,

July, 1935. According to said article the transit time damping is equal to Where S is the steepness of the characteristic curve which indicates the relation between the total current flowing through the control grid and the control grid voltage while or represents the, angular frequency of the high-frequency voltages applied and t the transit time of the electrons between the cathode and the control grid.

If, as is customary, the amplification of the system is regulated by causing the bias voltage of the control grids of the amplifying tubes to vary, the slope and therefore also the transit time damping have difierent values for every value of the amplification. If an oscillatory circuit is connected between the control grid and the cathode of one or more of the amplifying tubes, the damping of this circuit and therefore the selectivity of the system will be different for every value of the amplification.

A damping effect which depends on the steepness of an amplifying tube may be obtained, as is well-known, by connecting a resistance into the cathode lead of the tube.

In a system for amplifying electrical oscillations of very high frequency wherein the control grid and the cathode of one or more amplifying tubes are connected to an oscillatory circuit tuned to the frequency of the oscillations to be amplified, a selectivity which is independent of the amplification is obtained, according to the invention, by including in the cathode lead of the tube or tubes a resistance of such value that the variation of transit time damping with amplification is compensated for.

The invention will be explained more fully with reference to the accompanying drawing.

The drawing represents a screen grid tube wherein the control grid G and the cathode K are connected to a tuned oscillatory circuit consisting of an inductance L and a variable capacity C. The damping of the oscillatory circuit is represented by the parallel resistance R (shown dotted). The cathode lead of the tube includes a resistance R1; while the capacity between the control grid and the cathode is represented by Furthermore ic=iwC kV Consequently V=Vg+ (it +ic) Ric Vg[1+Rk(S+7'wCgk)] In parallel with the oscillatory circuit is consequently located an impedance:

The damping produced by the resistance R1: consequently amounts to m C R 51302 ulc k) With wave-lengths of about 6 to 12 meters ak k 1 For the damping caused by the resistance R1; one consequently finds approximately:

This damping has a positive term: w Cgk Rk which is not dependent on the steepness, and a negative and consequently relatively undamping term 2w cgk Rk S, which is proportional to the steepness. Now the value of the resistance Rk is so chosen that t 2C m/m If this condition is satisfied and the value of R1; does not turn out so great as to contradict assumptions (a) and (b) above, the total damping of the oscillatory circuit is:

This damping is consequently independent of the steepness of the amplifying tube, 1. e. the

selectivity of the system is independent of the bias voltages of the control grids of the amplifying tubes.

What I claim is:

1. System for amplifying electrical oscillations of very high frequency, wherein the control grid and the cathode of an amplifying tube are connected to an oscillatory circuit tuned to the frequency of the oscillations to be amplified, the cathode lead of said amplifying tube comprising a resistance of such value that the transit time damping is compensated for.

2. An amplifying system as defined in the preceding claim wherein the resistance is equal to ac lio r representing the transit time of the electrons between the cathode and the control grid, and Cgk, the interelectrode capacity between the control grid and the cathode.

. 3. A system for the amplification of high frequency oscillations comprising a vacuum tube amplifier having grid and cathode electrodes, a tunable circuit connected to said grid and cathode, and a bias resistance connected to the cathode, said bias resistance being so proportioned to the damping between said grid and cathode due to the transit time of the electrodes that the selectivity of the system is independent of amplification.

4. In combination, a vacuum tube amplifying circuit operating in a range of high frequencies at which the transit time of the electrons in the tube causes damping of the tube input circuit, said transit time damping varying with changes in the bias voltage applied to the control grid of the tube, and a resistance connected to the cathode of said tube and being of such value that the transit time damping is substantially independent of changes in the control grid biasing voltage.

5. In combination, a vacuum tube amplifying circuit operating in a range of high frequencies at which the transit time of the electrons in the tube causes damping of the tube input circuit,

- said transit time damping varying with changes in the biasing voltage applied to the control grid of the tube, a tuned circuit connected to the tube input, the transit time damping variations causing the selectivity of the tuned circuit to vary, and a resistance connected to the cathode of said tube and being of such value that the selectivity of the tuned circuit is made substantially independent of changes in control grid biasing voltage.

6. A system for the amplification of high frequencies comprising a vacuum tube amplifier provided with a plurality of electrodes including a control grid and a cathode, an input circuit connected between said control grid and cathode, said system operating at frequencies so high that the transit time of the electrons in the tube causes variations in the damping of tube input circuit with changes in the biasing voltage applied to the control grid, and means comprising a resistance connected to the cathode whereby the damping due to the electron transit time is substantially compensated for.

7. A system for the amplification of high frequency oscillations comprising a vacuum tube amplifier provided with a plurality of electrodes including an input control grid and a cathode, said system operating at frequencies so high that the transit time of the electrons in the tube.

causes appreciable conductance between said grid and cathode, said input conductance varying with changes in applied control grid bias voltage, a tunable circuit connected between said control grid and cathode and being affected by the variations in said input conductance to vary its selectivity, and means comprising a resistance connected to the cathode whereby said variation in input conductance is substantially compensated for, to provide a system in which the selectivity is independent of the changes in the bias voltage.

ALDERT VAN DER ZIEL. 7

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